Beerkens, Ruud G. C.

Faber, Anne-Jans

Muysenberg, Erik

Simonis, Frank

English

Repositorium für Naturwissenschaften und Technik

1. IntroductionGlassmaking is undergo ing rapid changes. Today's requi rements or challenges, so to speak, are increasinglydemanding : b o t h glass qual i ty and product ion Outputneed to be increased to higher levels, while, at the sametime, reducing energy consumpt ion , lowering emissionlevels, a n d increasing the rat io of cullet used. The basicquest ions are, of course: the technology is to fulfil allthese requirements a n d are the Solutions cost-effective?Look ing at the technological developments over the pastten years, it becomes clear tha t the glase industry is indeed involved in many new technologies. The glass in-dus t ry and its suppliers have begun to use advancedtools to opt imize p roduc t ion and products . Α strikingexample is the use of numerical Simulation tools for thedesign a n d control of the glass melt ing and glass form-ing processes as well as for the design and improvementof glass products . These Simulation models have now reached such a degree of reliability a n d applicability thatindustr ies no t only use t h e m for the purpose of gaininginsight, bu t actually per form opt imizat ion studies di-rectly linked to existing processes and product designs.Predict ion of glass quality, glass t ank Performance andproduc t behaviour are key elements.2. Modelling the glass melting processA b o u t 15 years ago, T N O - T P D star ted its modelling ac-tivities in the field of glass mel t ing technology. For a glass mel t ing tank , in fact a chemical reactor with manycomplex subprocesses, an adequa te process descriptionrequires a füll synthesis of all melting-related subpro-cesses. Wi th the suppor t of m a n y nat ional and inter-na t ional glass industries, T N O - T P D has addressed over80 man-years in the pas t 15 years towards bo th ma th -ematical model l ing of the mel t ing process as well astowards fundamenta l exper imenta l research in glassmelt ing chemistry. This has resulted in a glass t ankmode l wherein the specific glass melt-related processmodels have been fully coupled being linked as sub-models(figure 1).Received June 27, 1997.Lec ture o n the occas ion of the award ing of the Ot to-Schot t -Forschungspre i s on June 9, 1997 in Växjö (Sweden).T N O glass tank modelcombustion: air-fired oxy-fuel-firedbatch blanket: melting rheologyelectrical meltingelectrical boostingforced bubblingfoammain model: fmite volumecalculationscalculating: glass melt flows temperatures heat transfer for: any geometryand shape operatingparameters as pre-processor as post-processorparticle tracing: residence time quality indexdissolution: sand grains refractoryredox, dissolvedgases, chemicalequilibriabubble tracing: growth shrinkageoptimization (of design or process parameters),trouble shooting, tank controlFigure  1 . Schematic of T N O glass t a n k mode l with submodels .S tandard 3D computa t ional fluid dynamics for modelling flow and temperatures in the melt and combust ionspace is basic, but is insufficient to assess the effects ofprocess condit ions and furnace design on glass qualityand t ank Performance. Therefore, the au thors ' focus hasshifted more and more towards modell ing of the specificglass melt-related chemistry and physics, leading to sub-models for e. g. redox, dissolved gases, (re)fining, particle(sand grain, a lumina, knots) dissolution, homogeni-zation, volatilization, batch melting, glass defect back-tracing etc. Impor t an t issues are model verification bo thon laboratory and industrial scale as well as measure-ment of the required input data , chemical and physicalconstants such as diffusion coefficients, chemical equih-bria and solubilities.3. Output of glass tank modellingGlass t ank modell ing has proven to be a powerful opti-mization tool . It is now being used bo th by R & D expertsas well as by t ank Operators in the plants. The trackrecord of T N O - T P D glass t ank model Covers optimizat ion studies in more than 70 industrial glass tanks,ranging from container, float, TV, special, sodium Sili-cate to fiber glass tanks. Different combust ion Systems,Upgrading glass melting technology by model-based processing^^R u u d G. 0 . B e e r k e n s , A n n e - J a n s Faber, Erik M u y s e n b e r g a n d Frank S imon isTNO Institute of Applied Physics  Glass Technology Eindhoven (The Netherlands) ­-----------------------gas or oil, air or oxy-fuel firing, end-por t or side-portcan be handled. Criteria for optimizat ion usually arefirst, glass quality versus pull rate, second, process sta-bility, flexibility and efficiency, third, temperature loadof refractory, fourth, fast j o b changes, and fifth, re-duction of energy and emissions. Both stat ionary as wellas transient situations can be taken into account . TheOutput of glass t ank modell ing usually is a set of opt imalcharacteristics or best scenarios: improved tank design,burner system (kind and posi t ion of burners), oper-ational settings (e. g. heat distr ibution, pull rate, boost ingand bubbling location and intensity, fining agents), lo-cation of sensors, j o b change strategy or diagnosis ofprobable causes of glass defects.4. Constraints on useAlthough some models come very close to reality, models are by definition simplified descriptions of reality.Verification of their "fit for use" is often preferred beforegoing into optimization runs. This can be done e.g. byrunning base case simulations against existing glass t ankOperations. Process data such as bot tom/crown tempera-tures and residence time distr ibutions from existingmelting Operations are of course  a necessity. Often suchdata lack accuracy or appear no t reliable. O n the otherhand , some of the required model inputs are also no tvery well known unless the experimental effort in thelaboratory: there is an ongoing need for accurate meas-urement of glass melt da ta and properties.5. Trends and future developmentsWith the continuously increasing Computer speed, dou-bling every 1.5 years, the number of gridpoints is increasing simultaneously: ten years ago, a typical melterSimulation was carried out using 10 000 gridpoints,nowadays 300 000 to 1000 000 gridpoints are being usedfeaturing more accuracy and details. Fully coupledcombust ion-chamber melter calculations or coupledmelter /working end/feeder simulations are per formed .Instead of mainf rame Computers, now Workstat ions a rebeing used a n d even fast PC's. With in the next Comingyears, füll 3 D Simulation models will r u n fast e n o u g hto use t hem for model -based predictive control of glassmelting tanks . Coupl ing these models to contro l Systemsis one of the areas where T N O is active in at themomen t . Con t inuous model -based analysis of the r u n -ning mel t ing process by checking the process Outputdata against the Virtual mode l envi ronment will lead t omore intelligent moni to r ing and contro l of the process.Next to tha t the Simulation code is still unde r fur therdevelopment . Specific submodels are being further im-proved: ba tch modell ing, foam produc t ion and destabil i-zation, glass homogeneity. Also in the area of glass de -fects  a coupl ing between glass defect analysis a n d glassmelt ing model l ing is in development in order to o b t a i nan improved defect source analysis system including cor-rective actions.6. Spin-Off: up-to-date database for meltingtechnologyThe success of the glass melt ing mode l is strongly basedon the qual i ty of the glass melt-specific submode l sdescribing the characterist ic glass mel t ing p h e n o m e n a .These submodels de termine how close the real processcan be predicted. Assessment of existing mel t ing k n o w -how together wi th addi t ional fundamenta l research inthese areas has led to improved descr ipt ions for all melt-ing-related p h e n o m e n a . These descript ions are con-stantly upda ted and s t ructured to fit in the Virtual en-vi ronment of the melt ing model . T h e mode l itself hasbecome  a da tabase wherein latest deve lopments a n d insights in melt ing technology are stored. It therefore alsoplays  a role in the disseminat ion and upda t ing of mel t ingknow-how for all the internal and external users of themodel . To keep the experts experts, to keep glass technologists g o o d technologists.Address of the au thors :R. G. C. Beerkens, A.-J. Faber, E. Muysenberg , F. SimonisT N O Insti tute of Applied PhysicsD e p a r t m e n t Glass TechnologyΡ Ο. Box 595NL-5600 A N Eindhoven-----

Upgrading glass melting technology by model-based processing

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Upgrading glass melting technology by model-based processing

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